The invention relates to a printing unit for a machine for processing flat printing materials, in particular a sheet-processing rotary printing machine, having a feeding cylinder for loading the printing unit with the printing materials in a processing direction, and a device for removing particles adhering to the surface of the printing materials, the particle-removing device comprising a blast or blowing device for separating the particles from the printing materials without contact, and a suction device for discharging the separated particles. The invention also relates to a machine for processing flat printing materials and to a machine equipped with at least one such printing unit, and also a feeder drum for such a printing unit.
For satisfactorily printing flat printing materials, such as sheets, for example, particles adhering to the surface of the sheets must be removed. The particles are, in particular, dust, and possibly separating agents which prevent adjacent sheets in a pile or stack from adhering to one another, in a case wherein printing is performed in a second pass through a printing machine.
In order to dispose of such particles, suction brushes connected upstream of a printing nip have become known heretofore, which loosen the particles mechanically from the surface of the printing materials and removes them by vacuum or negative pressure. As a rule, the suction brushes are be arranged between the impression cylinder and a feeding drum or cylinder that transfers the printing material to the impression cylinder, in order to feed the printing material dust-free to the printing nip. In order to obtain a printed a image that is free of transverse stripes, the image should have been completely printed out at the time of transfer to a transfer device, such as a transfer cylinder, for example.
Disadvantageously, when using suction brushes, there is, on the one hand, a possibility of mechanical damage occurring to the printing materials, it being possible, moreover, for paper particles loosened as a result of abrasion to lead to the formation of hickeys or lint, so that the suction brush requires continual installation and removal in order to clean it and remove the hickeys. This applies in particular to sensitive printing materials and to repeated passes or throughput, respectively, during multicolor printing. On the other hand, the suction brush requires additional space in the overall construction space of the printing unit, which is limited in any case, so that the feeding drum has to be arranged at a relatively great distance from the printing nip, which results in the printing material, for example, transferred from a pregripper to the feeding drum and then to the impression cylinder, being deflected over large circumferential sections of the feeding drum and of the impression cylinder. In the case of relatively stiff printing materials, in particular, this leads to scratching and/or marking thereof. Furthermore, because of the space required for the suction brush arranged between the feeding drum and the printing nip, for a given inclination and output height of a feeding table providing the printing materials to the pregripper, guidance of the printing material on the feeding table so as to be tangential to the feeding drum is not possible, so that, in particular in the case of thin printing materials, as the latter are transferred to the feeding drum, there is a risk of forming an inlet corrugation, by the fact that the printing material, which is gripped at the leading edge thereof by the pregripper, is bent upwardly in a direction towards the feeding drum at the point of contact with the feeding drum. Otherwise, it would be necessary for a feeding table of given output height, from which the printing material is transferred to the feeding drum by the pregripper, to be built quite long due to the feeding drum being arranged relatively far below the impression cylinder, which would be complicated from a construction standpoint and costly.
The published German Patent Document DE 199 03 887 A1 describes a printing machine having a first printing unit for printing the front side of sheets and a second printing unit for printing the rear side. Both printing units are equipped with devices for cleaning the sheets to be printed, the cleaning devices being buildable, on the one hand, by suction brushes, and on the other hand, by non-contacting or contact-free devices, such as blowing-air or blast, suction or electrostatic devices. The disadvantages mentioned hereinabove result from the requirement for additional space demanded by the respective cleaning device.
It is accordingly an object of the invention to provide a printing unit with a device for removing particles, as described in the introduction hereto, in a simple and cost-effective manner and wherein the space required for the device for removing particles, which adhere to the surface of the printing material, is minimized. It is, furthermore, an object of the invention to provide an accordingly improved machine for processing flat printing materials equipped with such a printing unit, and to provide an improved feeding cylinder for such a printing unit.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a printing unit for a machine for processing flat printing materials, comprising a feeding cylinder for loading the printing unit with the printing materials in a processing direction, and a device for removing particles adhering to the surface of the printing materials, the particle-removing device further comprising a blowing device for separating the particles from the printing materials without contact, and a suction device for discharging the separated particles, both the blowing device and the suction device being formed by blowing and suction chambers arranged within the feeding An cylinder and having a fluidic connection to surroundings of a By jacket surface of the feeding cylinder.
In accordance with another feature of the invention, both the blowing chamber and the suction chamber extend at least approximately over the entire width of the feeding cylinder.
In accordance with a further feature of the invention, both the blowing chamber and the suction chamber are arranged fixed against rotation.
In accordance with an added feature of the invention, the printing unit further comprises lines received in the feeding cylinder at least approximately centrally with respect to the feeding cylinder, via which both the blowing chamber and the suction chamber are actable upon by positive and negative pressure, respectively.
In accordance with an additional feature of the invention, the blowing chamber is arranged upstream of the suction chamber with respect to the processing direction.
In accordance with yet another feature of the invention, the suction chamber directly adjoins the blowing chamber.
In accordance with yet a further feature of the invention, the suction chamber is connected to a larger section of the jacket surface of the feeding cylinder than is the blowing chamber.
In accordance with yet an added feature of the invention, the jacket surface of the feeding cylinder connected to the suction chamber extends over a sector angle between 30xc2x0 and 150xc2x0.
In accordance with yet an additional feature of the invention, the sector angle is between 60xc2x0 and 120xc2x0.
In accordance with still another feature of the invention, the jacket surface of the feeding cylinder connected to the blowing chamber extends over a sector angle between 1xc2x0 and 20xc2x0.
In accordance with still a further feature of the invention, the sector angle is between 1xc2x0 and 10xc2x0.
In accordance with still an added feature of the invention, the feeding cylinder forms a hollow cylinder having a multiplicity of boreholes extending through the jacket surface thereof.
In accordance with still an additional feature of the invention, the printing unit further comprises thin webs formed in the jacket surface of the feeding cylinder for carrying the printing materials.
In accordance with another feature of the invention, the thin webs are arranged at least approximately in the circumferential direction of the feeding cylinder.
In accordance with a further feature of the invention, at most 10% of the jacket surface of the feeding cylinder is occupied by the thin webs.
In accordance with an added feature of the invention, the percentage is at most 5%.
In accordance with an additional feature of the invention, the printing unit further comprises thin webs formed in the jacket surface of the feeding cylinder for carrying the printing materials, the boreholes and the thin webs following one another alternately in axial direction of the feeding cylinder.
In accordance with yet another feature of the invention, the printing unit further comprises a blowing air bar arranged at least approximately parallel to the axis of the feeding cylinder located downstream of the feeding cylinder with respect to the processing direction.
In accordance with yet a further feature of the invention, the printing unit further comprises an impression cylinder, the blowing air bar being disposed in a wedge which, on one side, is bounded by the feeding cylinder and, on the other side, is bounded by a section of the impression cylinder carrying the printing materials.
In accordance with yet an added feature of the invention, the blowing air bar has nozzles aligned in the direction of the printing materials carried by the impression cylinder.
In accordance with yet an additional feature of the invention, the nozzles of the blowing air bar are directed towards areas of the printing material carried by the thin webs on the jacket surface of the feeding cylinder.
In accordance with another aspect of the invention, there is provided a machine for processing flat printing materials, having at least one printing unit comprising a feeding cylinder for loading the printing unit with the printing materials in a processing direction, and a device for removing particles adhering to the surface of the printing materials, the particle-removing device further comprising a blowing device for separating the particles from the printing materials without contact, and a suction device for discharging the separated particles, both the blowing device and the suction device being formed by blowing and suction chambers arranged within the feeding cylinder and having a fluidic connection to surroundings of a jacket surface of the feeding cylinder.
In accordance with a further feature of the invention, the processing machine is a sheet-processing rotary printing machine.
In accordance with a concomitant aspect of the invention, there is provided a feeding drum for a printing unit for processing flat printing materials, comprising a device for removing particles adhering to the surface of the printing materials, the particle-removing device further comprising a blowing device for separating the particles from the printing materials without contact, and a suction device for discharging the separated particles, both the blowing device and the suction device being formed by blowing and suction chambers arranged within the feeding drum and having a fluidic connection to surroundings of a jacket surface of the feeding drum.
According to the invention, in a printing unit of the type mentioned at the introduction hereto, the object of the invention is achieved by forming both the blowing device and the suction device from blowing and suction chambers which are arranged within the feeding cylinder and which have a fluidic connection to the surroundings of the outer or jacket surface of the feeding cylinder.
By the fact that the device for removing particles adhering to the surface of the printing material is integrated into the feeding cylinder in accordance with the invention, the particle-removing device needs no additional installation space, so that in the case of a compact construction of the printing unit, the feeding cylinder can be arranged to be higher with respect to the impression cylinder than in the prior art, in order firstly to permit deflection of the printing material around a relatively small circumferential section of the feeding cylinder, and secondly to permit guidance of the printing material on the feeding table so as to be tangential to the feeding cylinder, while avoiding the formation of an inlet corrugation. In this way, any impairment both of stiff and also of thin printing materials is reliably avoided and the sheet guidance is in no way impeded, a slimmer sheet run being possible, in particular because the printing material wraps to a lesser extent around the feeding cylinder. As a result of the printing material being attracted by suction, it is moreover smoothed onto the jacket surface of the feeding cylinder, so that sheet smoothing takes place before the printing material is introduced into the printing nip. In this way, possible changes in shape of the printing material in the following printing nip are minimized, and thus ghosting is prevented to the greatest possible extent.
In order to free the entire width of printing material from adhering particles, both the blowing chamber and the suction chamber expediently extend at least approximately over the entire length of the feeding cylinder.
In a preferred embodiment, provision is made for both the blowing chamber and the suction chamber to be fixed against rotation, so that, on the printing material transferred to the feeding cylinder by a pregripper, for example, there always acts a stationary blown air flow for the contact-free separation of the particles from the printing material, and the printing material is then likewise acted upon in a stationary region by vacuum, which discharges the separated particles. Both the blowing chamber and the suction chamber can preferably be acted upon with positive and negative pressure, respectively, via lines arranged at least approximately centrally in relation to the feeding cylinder.
The blowing chamber is expediently arranged upstream of the suction chamber in the sheet conveying direction, in order firstly to separate without contact the particles adhering to the printing material and then to discharge them by vacuum while smoothing the printing material onto the feeding cylinder. In this regard, the suction chamber preferably adjoins the blowing chamber directly.
In an advantageous feature, the suction chamber is connected to a larger section of the jacket surface of the feeding cylinder than is the blowing chamber, the jacket surface of the feeding cylinder connected to the suction chamber preferably extending over a sector angle between 30xc2x0 and 150xc2x0, in particular between 60xc2x0 and 120xc2x0, and the outer surface of the feeding cylinder connected to the blowing chamber preferably extending over a sector angle between 1xc2x0 and 20xc2x0, in particular between 1xc2x0 and 10xc2x0.
The feeding cylinder is preferably formed by a hollow cylinder which has a large number of boreholes which pass through the jacket surface thereof, in order to connect this jacket surface at the respective circumferential section thereof to the blowing or the suction chamber.
The outer or jacket surface of the feeding cylinder is preferably equipped with thin webs which carry the printing material, so that the vacuum or blown air acts upon the largest possible surface area of the printing material. The webs are, for example, arranged at least approximately in the circumferential direction of the feeding cylinder, preferably at most 10%, in particular at most 5%, of the outer surface being occupied by the webs. The boreholes and the webs expediently follow one another alternately in the axial direction of the feeding cylinder.
In a further development of the invention, provision is made for a blowing air bar disposed at least approximately parallel to the axis of the feeding cylinder to be arranged downstream of the latter. This bar is preferably arranged in a wedge or wedge-shaped pocket which, on one side, is bounded by the feeding cylinder and, on the other side, is bounded by a section of the impression cylinder which carries the printing materials.
The blowing air bar serves for discharging the particles which may possibly remain on the printing material in the region of the webs, whereon it is in contact with the outer or jacket surface of the feeding cylinder, so that the particles which may possibly remain in these regions are distributed uniformly, and therefore no markings are produced on the printing material.
The blowing air bar has nozzles which are directed in particular in the direction of the printing materials, are expediently distributed over the entire length of the blowing air bar and are advantageously directed onto the areas of the printing materials carried by the thin webs on the outer or jacket surface of the feeding cylinder.
In addition, the invention also relates to a machine for processing flat printing materials, in particular a printing machine, which is equipped with at least one printing unit of the aforementioned type, and also a feeding cylinder for a printing unit of the aforementioned type.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a printing unit with a device for removing particles, and a machine for processing flat printing materials and having such a printing unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: